There is a growing requirement for alternate fuels for vehicle propulsion and power generation. These include fuels such as natural gas, bio-diesel, ethanol, butanol, hydrogen and the like. Means of utilizing fuels needs to be accomplished more efficiently and with substantially lower carbon dioxide emissions and other air pollutants such as NOxs.
The gas turbine or Brayton cycle power plant has demonstrated many attractive features which make it a candidate for advanced vehicular propulsion as well as power generation. Gas turbine engines have the advantage of being highly fuel flexible and fuel tolerant. Additionally, these engines burn fuel at a lower temperature than comparable reciprocating engines so produce substantially less NOx per mass of fuel burned.
A multi-spool intercooled, recuperated gas turbine system is particularly suited for use as a power plant for a vehicle, especially a truck, bus or other overland vehicle. However, it has broader applications and may be used in many different environments and applications, including as a stationary electric power module for distributed power generation.
The thermal efficiency of gas turbine engines has been steadily improving as the use of new materials and new design tools are being brought to bear on engine design. One of the important advances has been the use of ceramics in various gas turbine engine components which has allowed the use of higher temperature operation and reduced component weight. The use of both metallic and ceramic components in an engine which may have wide variations in operating temperatures, means that special attention be given to the interfaces of the these different materials to preserve the intended component clearances. Control of clearances generally leads to fewer parasitic performance losses. Fewer parasitic performance losses incrementally improves engine efficiency.
There therefore remains a need for innovative designs for gas turbine compressor/turbine spools fabricated from a combination of metallic and ceramic materials that maintain a desired control of clearances between various compressor and turbine components.